The invention is related to computer graphics and, in particular, a user interface using computer graphics for performing operations on a screen display.
A user interface provides, among other things, an interface between a computer user and an application program executing via an operating system of the computer. In the absence of a user interface, the computer user has to learn application program commands and/or operating system commands which often require some technical expertise and knowledge. Instead of entering line commands to run an application program, to add a peripheral device, to activate a "Web" browser to connect to the Internet's World Wide Web, etc., the user interface allows even a computer novice to carry out these and other operations on the computer with ease and simplicity.
It is well known that via the user interface the user can, for example, view, manipulate, etc. images and graphical objects on a display screen via an input device such a mouse, light pen, keyboard, joystick, etc. coupled to the computer. Various operations associated with the images and objects are available to the user. For example, by selecting ("clicking" on) a particular object ("icon") on the screen, the user may start running an application program, change a screen or a set-up configuration of the computer, manage files in various directories and sub-directories, etc. One of the operations that the user interface of an application program with graphical images may provide is a so-called "zoom" or "zooming" operation which is explained hereinbelow.
FIG. 1 shows a graphical universe 100 that is much larger than the display screen 102 of a computer monitor, television set, etc. The entire universe 100 may be available to the user for arranging, for example, various images/objects 104, 106, 108, 110 (as represented by icons) corresponding to application programs, images, files, etc. At a particular point in time, as shown in FIG. 1a, the user views only several objects 106, 108 at once. When the user wants to view the entire universe 100 on the display screen 102, all the objects 104, 106, 108, 110 in the universe 100 should "fit" on the display screen 102. To achieve this, he "zooms out" from his current display (picture) on the display screen 102. That is, the objects 104, 106, 108, 110 are reduced in size while maintaining their relative positions in the graphical universe 100, as shown in FIG. 1b. As further shown in FIG. 1b, the entire universe 100 appears on the display screen 102. Conversely, if the user is only interested in a detailed view of a particular object, he "zooms in" to the object-in-interest. That is, the object-in-interest (picture) is enlarged.
Several disadvantages, however, are associated with a conventional zoom operation. In particular, the user does not know whether either of the limits of zoom-in or zoom-out operation has been reached or where those limits are on the display screen. For example, when the user keeps zooming-in to the object or zooming-out from the object, he has no visual indication as to where the limits are or whether those limits have been reached whereby further zoom operations may be fruitless. In addition, the current size of objects on the display screen with respect to the upper (zoom-in) and lower (zoom-out) limits as provided by the computer system are not shown on the display screen, leaving the user to wonder about the extent of further zoom-in/out.
A need therefore exists for a user interface containing features which overcome the above-mentioned disadvantages and realize the criteria as discussed above.